In many industrial and municipal waste systems, waste water which is laden with grit is pumped from a primary recovery device in the waste stream to a secondary device (e.g., a cyclone separator) which further concentrates the grit. The stream may also pass through a third device (e.g., a screw conveyor) to further dry and concentrate the grit.
However, the waste water stream which enters the waste system often may include long sticks, cans, large solids, and other non-soluble debris. Such debris can disrupt, plug or stop any of the recovery devices from operating. For example, the debris can get into the pumps and piping in the system. It can span openings and wedge in openings, creating an obstruction. Further, smaller materials (e.g., stringy materials such as paper, paper towels, and rags) can get caught in the larger debris and eventually build up a dam that completely plugs pipes and openings. When that occurs, the plug has to be removed, which may require rodding or physically cleaning out the opening. During the process of removing such debris, it may be necessary to shut down the system. Shutting down the system for this purpose is, obviously, undesirable and inefficient.
Screens have therefore been used to block large debris from reaching the recovery devices with the entering waste stream, while still allowing flow through of the waste stream. Such screens require relatively large openings, however, to ensure sufficient waste stream flow, and thus opening sizes have varied from around ⅜″ square to 2″ wide space between parallel (vertical) bars. As a result, various items of relatively large trash or debris may still pass through the openings and into the recovery devices, including long sticks, tooth brushes and the like through even the square openings, and large objects as well as long sticks, etc. may pass through the larger long openings. Of course, large objects may also pass through to the recovery devices if the screens are not maintained properly, or if larger openings develop around the bottom of the screen.
Grit removal systems such as grit extractors or grit traps have been used in many waste systems to remove grit from the waste water prior to passing the water on to a recovery device of the system. For example, one advantageous apparatus includes flumes for injecting and extracting liquid tangentially relative to a round chamber, creating a circular flow stream which causes the grit to settle near the bottom center of the round chamber. That grit in the injected liquid is thus removed from the liquid stream and collected in the storage chamber for relatively easy removal. Such an apparatus is disclosed in U.S. Pat. No. 6,811,697 B2, the full disclosure of which is hereby incorporated by reference.
U.S. Pat. Nos. 3,941,698, 4,107,038 and 4,767,532 also disclose grit extractor apparatuses. The disclosures of all of these patents are also hereby fully incorporated by reference.
For example, U.S. Pat. No. 4,767,532 discloses an apparatus for removing grit in which a grit storage chamber is provided beneath the center of the round chamber of the grit removal system. A removable plate substantially aligned with the floor of the round chamber generally separates the two chambers, with a central opening through the plate permitting communication between the chambers. A cylindrical shaft is rotatably supported on its upper end above the round chamber and extends down through the round chamber through the plate central opening. Liquid flow in the round chamber causes grit particles to settle toward the chamber floor, where they are urged radially inwardly so as to drop through the plate central opening into the grit storage chamber. A multi-bladed propeller is mounted on that shaft above the plate, and rotates with the shaft to assist in the liquid flow to move the grit toward the plate center opening. A pipe also extends down through the cylindrical shaft into the grit storage chamber, and a pump is provided on the upper end of the pipe to allow grit in the bottom of the storage chamber to be removed by pumping up through the pipe.
In addition to the plate with a central opening as described above, grates, perforates plates, and the like have also been used to separate the chambers while still permitting grit to pass into the grit storage chamber from the round chamber. Such grates, etc. inhibit the flow of grit and debris into such chambers, and also build up a covering which closes off the opening. This not only requires manual unplugging of piping and openings from time to time, but also causes grit which is inhibited from moving into the grit storage chamber to undesirably pass through the grit removal apparatus altogether.
The present invention is directed toward overcoming one or more of the problems set forth above.